Many wells are drilled in reservoirs that have multiple pay zones. To stimulate each zone effectively it is crucial that the stimulation fluid, for example, fracturing fluid, be diverted to the targeted zone. It is common to use mechanical isolation to help ensure effective stimulation of each zone or groups of closely spaced zones. Normally it involves the following steps:                1. Perforate the lowest zone, then perform the hydraulic fracture treatment;        2. Flowback the stimulated zone;        3. Mechanically isolate the stimulated zone and then repeat the processes of fracturing and flowback; (and possibly a third or more zones when needed); and        4. Finally, remove the mechanical isolation devices, and put the well on production.        
Mechanical isolation methods are generally reliable for diverting multi-staged fracture treatments. However, extra work-over equipment is needed to set and remove the mechanical isolation devices in the well, thus, making such methods time consuming and expensive.
Another type of isolation method involves the use of sand plugs to isolate the treated zones. Such a method involves fracture treating the lowest zone, and then setting a sand plug across the lower zone to isolate the treated zone. The upper zone is then perforated and fracture treated. The process is repeated. Setting the sand plug is achieved by pumping sand slurry into the well and allowing sands to settle to the bottom. The permeability of the sand plug should be low enough to ensure that it would not allow the re-fracturing of the lower zone. The sand plug method is simple, less time consuming and economic. Unfortunately, this method is incapable of isolating zones in horizontal wells, as gravity pulls sands away from upper part of the well.
In recent years, drilling horizontal wells in combination with multi-staged fracturing has become a common practice, especially for tight formations including shale formations. In order to effectively fracture the targeted formation, zone isolation using mechanical means normally has to be applied in a horizontal well, despite the fact that it is time consuming and expensive.